Welding control using fuzzy logic analysis of video imaged puddle dimensions

ABSTRACT

A welding system includes an imaging system that takes frame by frame pictures of a weld puddle. The imaging system is located in the weld torch. From the images puddle length and width are determined. The length and width are applied against stored membership functions that cover a range of different weld current characteristics and the degree of membership of each dimension in those functions is determined, producing an alpha factor for each membership function. This provides a fuzzy current requirement. Stored values for moment and area for each membership function are multiplied by the alpha for the respective function. The total of the moments is divided by the total of the areas to produce a desired weld current. The weld head includes a weld wire feeder that is driven by a servo by which the wire can be feed along either side of the weld joint. The wire feeder is gear driven in such a way that it does not interfere with the optics in the weld torch. The optics include a strobe to illuminate the puddle. Signal processing includes a process for interpolating the puddle centerline from the range in puddle widths over successive strobed images of the puddle. The head is positioned automatically over the centerline.

.Iadd.The United States Government may have certain rights in thisinvention pursuant to Contract No. F 33657-89-C-2232 with the Departmentof the Air Force. .Iaddend.

TECHNICAL FIELD OF THE INVENTION

This invention relates to automated GTAW (gas tungsten arc welding)using computer based signal processing and programmed logic to controlwelding functions, in particular, welding control using fuzzy logicanalysis of video imaged puddle dimensions.

BACKGROUND OF THE INVENTION

GTAW is a widely used welding process in which an electric arc is formedby a welding torch, a shroud of inert gas, such as argon, is appliedfrom the torch to the weld area and a weld material, such as titanium or17-4 PH stainless .Iadd.steel.Iaddend., is supplied as a relatively thinwire. The weld and filler material forms a so-called "puddle" in theweld area, e.g., the space or joint between two pieces. Thecharacteristics of the puddle are dependent on the type of wire, weldmaterial, thickness and heat sink properties. Stainless steel is knownto produce a weld bead that has waves or ripples to the eye. Titaniumflows more easily, producing a generally smooth weld bead.

The characteristics of the puddle indicate the integrity of the weld inthe sense that if the arc is too hot, the puddle will be larger. Thetemperature of the arc is determined by the arc current. The currentheats the work-piece and the size of the puddle is a function of thetemperature in the weld area. More current is needed to maintain thework-piece weld area at a given temperature as the work-piece getsthicker, and conversely, if the material thickness decreases, the weldarea will get hotter. This can lead to changes in puddle width,indicating the change in the materials thickness. Thus, the weldcharacteristics will change as the work-piece's thickness changes. Evensmall changes in the thickness can produce undesired changes in the weldstrength, not to mention, that uneven heating can produce localvariations in material qualities of the workpiece, because areas thatare heated to a higher temperature may undergo slightly more removal ofimportant material components. An ideal weld provides a uniform weldbond and minimal material damage.

Experienced welders know those characteristics and visually inspect theweld puddle during the welding process. In a totally manual process, awelder controls the current input as well as the torch height and theamount of wire. The welder slowly moves the welding torch along thejoint manually controlling the time spent, wire feed rate and arcintuitively to achieve what visually appears to be a uniform puddle withthe correct dimensions.

Automated GTAW, also in use, attempts to provide more uniform welds bycontrolling temperature, motion of the head and wire feed rates. Forexample, U.S. Pat. No. 4,724,302, describes .[.a.]. an automated weldingprocess that maintains certain bead dimensions within specified rangesto achieve proper weld strength. There, the system employs a method ofautomatically controlling a weld bead (puddle) based on thecharacteristics of the bead height and width using interpolated valuesof bead height and width. For the most part, this approach typifiesthose that employ Boolean logic, one in which a particular object, forexample a variable, is or is not a member of a given set of parameters.Traditional systems, in other words, have used rigid "set theory" usingcrisp values.

Welding is an area of technology that is particularly suited toapproaches that do not use rigid Boolean set theory, but instead usesset theory in which a particular parameter has a degree of membership inone or more groups. This approach imitates human thinking and is called"fuzzy logic", in contrast with rigid Boolean logic that is thefoundation of tradition computational control systems.

Fuzzy logic was introduced by Zadeh in 1965, and, generally speaking,deals with such inherently fuzzy human concepts as "very, most, few" butas applied in a rigid mathematical framework. This may be called "fuzzysubset theory". The application of fuzzy logic to systems that have usedBoolean set theory in the past, has produced the fast growing field ofso-called "artificial intelligence". The objective of these systems itto .[.capturing.]. .Iadd.capture .Iaddend.the knowledge of the humanexpert in a particular problem area, representing it in a modular,expandable structure and transferring it to others. The process involvesconsidering the questions of process physics, knowledge acquisition,knowledge representation, inference mechanism, control strategies, userinterfaces and uncertainty. The issue of uncertainty, which humanknowledge intuitively always considers, is the essential issue in thedesign of fuzzy logic systems, and for a simple reason, much of theinformation in the knowledge base of a human is imprecise, incomplete ornot entirely reliable--in other words, uncertain. For instance, in GTAW,the weld quality is the desired end but is reflected in some way, notprecisely known or understood, in the puddle dimensions.

The harsh, small and unusual environment in which welding takes placepresents vexing problems in effectively applying a fuzzy logic basedprocess control approach. For example, problems arise in sensing ordetecting the characteristics of a molten metal puddle in the presenceof an electric and an inert gas cloud.

DISCLOSURE OF THE INVENTION

The objects of the present invention include providing an improved GTAWwelding system using fuzzy logic control with a reliable way to measurethe puddle and a flexible way to apply the weld wire into the puddle.

According to the present invention, optical snapshots are made of thepuddle during welding through a camera mounted in the weld torch. Thesesnapshots are optically filtered to identify the puddle from thesurrounding work-piece. The puddle is optically scanned and digitalsignals are produced which represent the weld puddle dimensions. Thosedimensions arm processed to determine their degree of fit in definedmembership functions. Weld current levels are assigned to differentdegrees of fuzzy membership functions based on puddle dimensions, suchas "big positive", meaning a decrease in current is needed because thepuddle is very big, or "big negative", meaning a current increase isneeded because the puddle is very small. Each membership function isdefined by several parameters. The membership functions over-lap(following conventional fuzzy logic principles). A "moment" value, a"centroid" and an "area" are assigned to each membership function. Therelationship between these is:

    Moment=Centroid·area                              (1)

The area for each membership function is the same. Each membershipfunction is defined by a range for a paddle dimension. For instance,each membership function is defined by an x value that defines adimension (width or length) calling for a big decrease in current and adegree of membership or fit in the function for that dimension as anassociated y coordinate. For a particular measured puddle dimension, the"degree of fit" is the alpha (α) value, a value is then applied to eachrule using preset values for "moment" and "area" for the rule to yieldcurrent values:

    Current moment=α·moment                     (2)

    .[.Current area=αarea.]. .Iadd.Current area=α·area .Iaddend.                                                 (3)

Total current is then compared to the actual current to produce an errorthat is used to modify the actual current to achieve the total current.##EQU1##

According to the present invention, additional fuzzy logic subsets areused for puddle length and the current area and current moment arecomputed from each of those sets in which the measured dimensions fall.For example, the puddle width may be BN (very narrow, calling for a bigincrease in current) but the length may be BP (very wide, calling for abig decrease in the current). By computing the alpha for each rule inwhich the measured dimension falls, and selecting one of the alphavalues, the moment and area for the rule are determined, the totalcurrent being determined from the sum of all moments and areas for rulesthat are selected (that "fire").

According to the invention, there are five rules used for titaniumwelding with filler addition and twenty-five rules for stainless steelwith filler addition.

According to the invention, the weld torch contains a wire feed that maybe the weld puddle during the weld process to adjust the wire feedposition relative to the weld direction. The head contains a gear systemcoupled to a servo motor.

According to the invention, a plurality of puddle values for length andwidth are obtained from the optical view of the puddle. Some of thesevalues are discarded in-a computational process that determines thecenterline of the puddle based upon the distribution of the puddlewidths over several successive scans.

Among the features of the present invention is that it provides anextremely precise and repeatable weld and minimizes excessive.[.energy.]. .Iadd.weld .Iaddend.input temperatures. Another feature isthat the invention provides a versatile wire feed arrangement forrobotic GTAW welders.

Other objects, benefits and features of the invention will be apparentto one of ordinary skill in the art from the following.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is fuzzy logic membership function definitions that are used todetermine weld current based on puddle width according to the presentinvention.

FIGS. 2 and 3 are fuzzy logic membership function definitions that areused to determine weld current based on puddle width and lengthaccording to the present invention.

FIG. 4 is a schematic of a robotic welder embodying the presentinvention.

FIG. 5 is a an elevation of a GTAW welding torch embodying the presentinvention.

FIG. 6 is a perspective view of the torch shown in FIG. .[.2.]. .Iadd.5.Iaddend.that includes a cut-away portion exposing wire feedtransmission and feed through optics embodying the present invention.

FIG. 7 is a function block diagram of an imaging system for providingsignals indicating puddle width and length according to the presentinvention.

FIG. 8 shows a frame of a puddle as imaged according to the presentinvention.

FIG. 9 is a table showing different puddle geometries and the associatedfuzzy logic rules used in the present invention based on thosegeometries.

FIG. 10 is a simplified block diagram of the control weld controlfunctions embodied by the present invention.

FIG. 11 is a table showing "moments" and "areas" for "fuzzyifying" and"defuzzifying" the required weld current according to the presentinvention.

.[.FIGS..]. .Iadd.FIG. .Iaddend.12 is a flow chart showing the steps forcomputing weld current using the fuzzification and defuzzificationsignal processing as taught by the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Fuzzy Logic Rules for two different metals

The use of adjectives to describe a problem is one key to fuzzy logic'sability to accommodate ambiguity. Adjectives describe an application'sfuzzy aspects. For example, what does a person mean when using termslike "small", "large" or "O.K."?

Membership functions and rules provide the ability to handle .[.completecombinations.]. .Iadd.complex relationships .Iaddend.easily, which is animportant benefit of fuzzy logic. An application's rules and membershipfunctions also contain the expert's knowledge about a system.

The adjectives used to formulate rules are more rigorously defined inthe application's membership functions. The shapes of the membershipfunctions are generally triangular and trapezoidal. When a processorscans an application's rule base, it tests each rule to determinewhether its IF conditions have been satisfied. When the if conditionsare met, execution branches to the rule's THEN path and the rule then"fires".

The control system's logic may be fuzzy, but measured inputs from aphysical system, and the outputs required to control it will be precise.Precise values in fuzzy logic systems are termed "crisp".

During program execution of a fuzzy system, several rules may fire andcontribute to the output. The output values mast then be resolved toyield a crisp value. To derive a precise value from multiple ruleexecutions, a method called "defuzzification"--obtaining a crisp outputvalue from a group of membership functions--is used. The defuzzificationmethod used in the welding system is the "centroid" or "center ofgravity" method. The method requires overlaying the portions of outputmembership functions produced by several rules and calculating thecenter of gravity of the resulting .[.shaped.]. .Iadd.shape .Iaddend.asthe final output value.

Fuzzy logic is an extension of traditional Boolean logic, while Booleanlogic requires a statement or condition to be either completely TRUE orcompletely FALSE. Fuzzy logic allows partial truth and potentialfalseness.

Fuzzy logic is derived from the more general theory of fuzzy sets.Functions in a welding system are created relating "measured weld puddlewidths" to "acceptable weld puddle widths". Thus, it can be calculatedthat the measured weld puddle width is 60% TRUE and 40% FALSE, forexample.

An assertion being simultaneously TRUE and FALSE is often a difficultconcept for someone used to working with Boolean logic, but .Iadd.the.Iaddend.world tends to be more "gray" than "black and white". Usingfuzzy sets to represent the weld puddle widths, it then can be said thatthe function relating to acceptable width is a curve relating to adegree of membership in the fuzzy sets defined.

Using only puddle width

As an example, there are five titanium rule sets, according to theinvention, which map as shown in FIG. 1:

Rule 1:

If measured weld puddle width is BN (big negative) THEN current is BP(big positive).

Rule 2:

If measured weld puddle width is N (negative) THEN the current is P(positive).

Rule 3:

If measured weld puddle width is Z (O.K.) THEN the current is Z (O.K.).

Rule 4:

If measured weld puddle width is P (positive) THEN the current is N(negative).

Rule 5:

If measured weld puddle width is BP (big positive), THEN current is BN(big negative).

These rules overlap as shown in FIG. 1, which show the five membershipfunctions based on weld puddle width and degree of membership.

EXAMPLE 1 Using Only Width

Referring to FIG. 1, if the measured weld puddle width that is measuredusing the coaxial vision system is 0.355 wide, this measured puddlewidth value maps to two membership functions: P(positive) .[.an.]..Iadd.and .Iaddend.BP(big positive). As shown the "P" and "BP"membership functions are defined as follows:

P=0.320 to 0.360

BP=0.340 to 1.00

Two membership functions are operated on in this example: the 0.355.[.measure.]. .Iadd.measured .Iaddend.puddle width maps to the degree ofmembership of 0.4 for .[.BP.]. .Iadd.P .Iaddend.and 0.6 for .[.P.]..Iadd.BP.Iaddend.. The 0.4 and 0.6 indicates the degree of membershipfor each fuzzy logic membership function that the 0.355 maps into.Therefore, the actual measured width belongs to two membership functionsor membership sets.

When two membership functions are involved, the membership function usesan average, weighted by the respective degree of membership values tocalculate the crisp or defuzzified output.

Following through with the example above, the crisp current output value(the defuzzified value) I is calculated as follows, where dgm. meansdegree of membership, mn. means moment: ##EQU2## Basic defuzzificationformula to solve for weld current

The area and the moment definition are application specific and aredependent on the process physics, materials, and the welded processcontrol equipment. For welding titanium the moments and area are definedas follows:

    ______________________________________                                        Membership                                                                    Function         Moment  Area                                                 ______________________________________                                        BN               -2.0    2.0                                                  N                -1.0    2.0                                                  Z                0       2.0                                                  P                1.0     2.0                                                  BP               2.0     2.0                                                  ______________________________________                                    

Finally, the defuzzified output is then added to the actual current toachieve the new required current.

    New current=actual current+defuzzified current             (6)

The new current value is used to adjust the systems current output usingfeedback control, as described below.

Using length and width

In the case of the 17-4 PH material, the rule sets become morecomplicated because the length of the weld puddle and the width of theweld puddle are used in the fuzzy logic calculation. Also, anintersection of sets of the degree of membership is incorporated in thecalculations.

The 17-4PH rule sets are as follows, as defined from FIGS. 2 and 3

Rule 1:

IF the measured weld puddle width is BN and the measured weld puddlelength is BN, THEN current is BP.

Rule 2:

IF the measured weld puddle width is BN and the measured weld puddlelength is N, THEN current is P.

Rule 3:

IF the measured weld puddle width is BN and the measured weld puddlelength is Z, THEN current is P.

Rule 4:

IF the measured puddle width is BN and the measured weld puddle lengthis P, THEN current is P.

Rule 5:

IF measured weld puddle width is BN and measured weld puddle length isBP, THEN current is P.

Rule 6:

IF measured weld puddle width is N and measured weld puddle length is BNTHEN current is P.

Rule 7:

IF measured weld puddle width is N and measured weld puddle length is N,THEN current is P.

Rule 8:

IF measured weld puddle width is N and measured weld puddle length is Z,THEN currant is P.

Rule 9:

IF measured weld puddle width is N and measured weld puddle length is P,THEN current is Z.

Rule 10:

IF measured weld puddle width is N and measured weld puddle length isBP, THEN current is Z.

Rule 11:

IF measured weld puddle width is Z and measured weld puddle length isBN, THEN current is Z.

Rule 12:

IF measured weld puddle width is Z and measured weld puddle length is N,THEN current is Z.

Rule 13:

IF measured weld puddle width is Z and measured weld puddle length is Z,THEN current is Z.

Rule 14:

IF measured weld puddle width is Z and measured weld puddle length is P,THEN current is Z.

Rule 15:

IF measured weld puddle width is Z and measured weld puddle length isBP, THEN current is N.

Rule 16:

IF measured weld puddle width is P and measured weld puddle length isBN, THEN current is Z.

Rule 17:

IF measured weld puddle width is P and measured weld puddle length is N,THEN current is Z.

Rule 18:

IF measured weld puddle width is P and measured weld puddle length is Z,THEN current is Z.

Rule 19:

IF measured weld puddle width is P and measured weld puddle length is P,THEN current is N.

Rule 20:

IF measured weld puddle width is P and .[.light.]. .Iadd.length.Iaddend.is BP, THEN current is N.

Rule 21:

IF measured weld puddle width is BP and measured weld puddle length isBN, THEN current is BN.

Rule 22:

IF measured weld puddle width is BP and measured weld puddle length isN, THEN current is N.

Rule 23:

IF measured weld puddle width is BP and measured weld puddle length isZ, THEN current is N.

Rule 24:

IF measured weld puddle width is BP and measured weld puddle length isP, THEN current is BN.

Rule 25:

IF measured weld puddle width is BP and measured weld puddle length isBP, THEN current is BN.

EXAMPLE 2 Using Length and Width

The following example will demonstrate the use of these rules for 17-4PH stainless .Iadd.steel .Iaddend.or any other material producing apuddle with observable length and width that are indicative of the weldquality in a real time mode.

Assume that the observed weld puddle length=0.310 and the measure weldpuddle width=0.225. Using the membership functions in FIGS. 2 and 3, the0.310 weld puddle length maps as follows: It has two fuzzy logicmembership functions. Rule 1) the weld puddle length is in P with amembership of 0.6 and Rule 2) the weld puddle length is also in Z with amembership there of 0.5. For the weld puddle width of 0.225, the widthmaps to two fuzzy logic membership functions as well: Rule 3) in thefunction for Z, with a degree of membership there of 0.3 and Rule 4) inthe function N, with a degree of membership of 0.8. In this case thesefour (4) out of the above twenty five (25) rules will fire: Rule 8, 9,13, and 14. The computation for current assumes these notations: min=theminimum value function (alpha)

    ______________________________________                                        min = the minimum value function (alpha)                                      MPW.sub.-- X                                                                  MPW = the measured puddle width                                               .sub.-- X = the mapped weld puddle width membership function                  MPL.sub.-- X                                                                  MPL = the measured puddle length                                              .sub.-- X = the mapped puddle length membership function                      Imoment.sub.-- X                                                              I = current                                                                   moment.sub.-- X = the weld current membership function                        Iarea.sub.-- X                                                                I = current                                                                   area.sub.-- X = the weld current membership function                          ______________________________________                                         Table of .sub.-- X Notations                                                  BN = Big negative                                                             N = Negative                                                                  Z = Zero                                                                      P = Positive                                                                  BP = Big Positive                                                        

For each rule, individual elements or components (μ_(m)(moment) andμ_(a)(area) of the total area and moment for the total current arecomputed for those rules that "fire", for example:

    ______________________________________                                        Rule 8:  μ.sub.m8 = (min(MPW.sub.-- N, MPL.sub.-- Z)                                × (Imoment.sub.-- P))                                                   μ.sub.a8 = (min(MPW.sub.-- N, MPL.sub.-- Z)                                × (Iarea.sub.-- P))                                            Rule 9:  μ.sub.m9 = (min(MPW.sub.-- N, MPL.sub.-- P)                                × (Imoment.sub.-- Z))                                                   μ.sub.a9 = (min(MPW.sub.-- N, MPL.sub.-- P)                                × (Iarea.sub.-- Z))                                            Rule 13  μ.sub.m13 = (min(MPW.sub.-- Z, MPL.sub.-- Z)                               × (Imoment.sub.-- Z))                                                   μ.sub.a13 = (min(MPW.sub.-- Z, MPL.sub.-- Z)                               × (Iarea.sub.-- Z))                                            Rule 14  μ.sub.m14 = (min(MPW.sub.-- Z, MPL.sub.-- P)                               × (Imoment.sub.-- Z))                                                   μ.sub.a14 = (min(MPW.sub.-- Z, MPL.sub.-- P)                               × (Iarea.sub.-- Z))                                            ______________________________________                                    

In these expressions, the degree of membership for each dimension ismapped to appropriate membership functions for the measured length andwidth and the lesser of the two (the "min" expression) is selected as amultiplier for the moment and area for the function. From those values,the "crisp" or "defuzzified" current value (I) is computed: ##EQU3##From this value, the new current is the sum of the actual current andthe crisp value:

    New current=actual measured current+I                      (8)

System Operation

FIG. 4 shows a robotic welding arm 10 on a base .Iadd.12 .Iaddend.and acontroller 14 that includes a monitor 16 for providing real-time graphicinformation of weld operation, such as the view of the weld puddle shownin FIG. 8. A weld (e.g., GTAW) torch 20 (see also FIG. 6) is located atthe end of the arm 10, and includes an electrode 22 for providing thearc current that heats a joint 24 on a work-piece 26. Inert gas issupplied around the electrode 22 from a supply 13. The current isprovided from a power supply .[.(Ps).]. .Iadd.(PS) .Iaddend.15, which iscontrolled by the controller to produce the required current accordingto the fuzzification and defuzzification process explained previouslyand the basic program steps described below:

Weld wire 28 is fed from a line feed motor 31 through a rotatable wirefeed arm 29, melting to form the puddle, which has a rippled or wavypattern as shown, the characteristic of 17-4 .Iadd.PH .Iaddend.weldmaterial. (When Titanium is used the puddle is generally smooth.)Optical filters 40 lie in the path between the camera and thework-piece, as illustrated in FIG. 7.Iadd.. .Iaddend.A second motor 30rotates and, through the gears 32 and 34, rotates wire guide arm 29,whose position is sensed by a position sensor .[.31.]. .Iadd.33.Iaddend.coupled to the arm (e.g. circular gear rack and pinion, asshown, or a timing belt) around a torch optics section 36, whichcontains, as shown in FIG. 7, a strobe 38, optical filters 40 and acharge coupled (CCD) video camera 42. The filters narrow the bandwidthof the optical and infra red energy that reaches the camera, mainlylimiting the energy to light in the wavelength range of the strobe 38.Strobe light is pulsed at a frequency determined by a strobe signal SSfrom a signal processor (not shown in FIG. 4, but 50 in FIG. 10) on theline 44a. In terms of the optics, the result is the snapshot of the weldpuddle as shown in FIG. 8, which may have any of the characteristics,over several snapshots, of length and width shown in the fuzzy logicrules shown in FIG. .[.8.]. .Iadd.9.Iaddend..

With the aid of FIG. 10, it can be additionally observed that theoverall system includes a microcontroller/signal processor 50 with amemory (MEM) 52 to store retrievable values corresponding to 1) themembership function shown in the fuzzy logic table (FIGS. 1, 2 and 3);and 2) the area and moment of each set BN, N, Z, P and BP (FIG. 11). Thesignal processor 50 also includes an input/output section or interfacefor signal transceiving. The microcontroller receives from the currentcontrol 54 a signal, Current Out, indicating the weld current I, andprovides a signal, Calculated Current, which is generated using thefuzzification and defuzzification signal processing described abovebased on the strobed image produced from an optics section 56. Thecurrent is provided from a power supply 58. A signal, Wire Feed.[.Position.]. .Iadd.Velocity.Iaddend., is provided from a wire feedposition sensor 60. The motor 30 receives a signal, Commanded .[.WireFeed.]. .Iadd.Arm .Iaddend.Position, to place the wire feed .Iadd.arm.Iaddend.in a desired location at which the difference between the.[.wire feed.]. .Iadd.arm .Iaddend.location signal and the commanded.[.wire feed.]. .Iadd.arm .Iaddend.location is zero.

The flow-chart shown in FIG. 12, illustrates the steps employed by thesystem controller, through the signal processor .[.14.]. .Iadd.50.Iaddend.using the previously described fuzzification anddefuzzification relationships when welding the seam 18 in FIG. 6. Afteran initialization step S1, a number of flames of the puddle are obtainedthrough successive strobing, providing puddle dimension data in step S2,for instance the length .[.an.]. .Iadd.and .Iaddend. width described inabove example 2. In step 3, the puddle width data is processed to yieldthe puddle centerline base .[.up.]. .Iadd.upon .Iaddend.the range ofpuddle width. At the following step S4, the membership tables, e.g.,FIGS. 1, 2 and .[.2.]. .Iadd.3 .Iaddend.are addressed by mapping thelength and width to the membership functions, producing the degree ofmembership or alpha values. These values .Iadd.are .Iaddend.stored instep S5, and in step S6 the area and moment for each function with analpha greater than zero is recalled. At step S7, the current .[.I.]..Iadd.area and moment .Iaddend.for each function with an alpha greaterthan zero is computed using .[.equation 6.]. .Iadd.equations 2 and 3.Iaddend.and the steps described.[.,.]. in either example 1 or 2 above.The values for I are summed in step .Iadd.S8 .Iaddend.and the sum ortotal is compared with the actual current (current out in FIG. 10) instep S9, producing an error signal, which the signal processor 50 usesin step S10 to compute the required change in current to bring the errorto zero in step S9.

One of ordinary skill in the art, having the benefit of this discussionof the invention and its embodiments, may be able to make modifications,in whole or in part, to those embodiments without departing from thetrue scope and spirit of the invention.

We claim:
 1. A welder comprising a welding torch on a controlled roboticarm, imaging means in the torch, a wire feeder on the torch and a weldcontroller for controlling the position of the torch and electriccurrent supplied by the torch, characterized in that:the weld controllercomprises signal processing means for producing a first signalindicating a weld dimension in response to an output signal from theimaging means produced by the weld puddle; for providing from aplurality of stored logic sets and in response to the first signal asecond signal indicating a degree of membership in a first set callingfor a first current change and a third signal indicating a degree ofmembership in a second set calling for a laser change in current; forproviding a fourth signal that represents the product of the secondsignal and a first stored area value .[.associated with said fistset.].; for providing a fifth signal that represents the product of thethird signal and a second stored area value .[.associated with thesecond set.].; for providing a sixth signal that represents the productof the second signal and a .Iadd.first .Iaddend.moment value .[.for thefirst set.].; for providing a seventh signal that represents the productof the third signal and a .Iadd.second .Iaddend.moment value .[.for thesecond set.].; and for providing an eighth signal that represents the.[.value.]. .Iadd.sum .Iaddend.of the sixth signal .Iadd.and the seventhsignal .Iaddend.divided by .Iadd.the sum of .Iaddend.the .[.seventh.]..Iadd.fourth .Iaddend.signal .Iadd.and the fifth signal .Iaddend.toinitiate a change in the electric current.
 2. The welder described inclaim 1, further characterized in that: there are five of said storedlogic sets, a first set defining an increase in current of a first levelfor a first range of puddle dimensions, a second .Iadd.set.Iaddend.defining an increase in current of a second level, less thanthe first level, for a second range in puddle dimensions including someof the dimensions in said first range, a third .[.range.]. .Iadd.set.Iaddend.indicating no change in current for a third range of dimensionsincluding some of the dimensions in said second range, a fourth setdefining a decrease in current of said second level for a fourth rangeof puddle dimensions including some of the dimensions in said thirdrange; and a fifth set defining .[.an.]. .Iadd.a .Iaddend.decrease incurrent of said first level for a fifth range of puddle dimensionsinclude some dimensions in said fourth range.
 3. The welder described inclaim 1, further characterized in that the dimension is puddle width. 4.The welder described in claim 1, further characterized in the wire feedis rotatable about the axis of the weld torch and includes a servo driveresponsive to signals from the signal control to index the wire feed tolocations on opposed sides of the puddle.
 5. The welder described inclaim 1, further characterized in that the imaging means providingsuccessive video frames of the puddle and the signal processing meanscomprises means for determining the centerline of the puddle from saidimages to provide a first centering signal for centering the weld torchover the puddle.
 6. A welder comprising a welding torch on a controlledrobotic arm, imaging means in the torch, a wire feeder on the torch anda weld controller for controlling the position of the torch and electriccurrent supplied by the torch, characterized in that:the weld controllercomprises signal processing means for producing a first signalindicating a weld puddle length and width in response to an outputsignal from the imaging means from the weld puddle, for providing from aplurality of stored logic sets and in response to the first signal asecond signal indicating a degree of membership in a first set callingfor a first current change and a third signal indicating a degree ofmembership in second set calling for a lesser change in current; forproviding a fourth signal that represents the product of the secondsignal and a first stored area value associated with the first set, andfor providing a fifth signal that represents the product of the thirdsignal and a second stored area value associated with the second set;for providing a sixth signal that represents the product of the secondsignal and a stored moment value for the first set; for providing aseventh signal that represents the product of the third signal and astored moment value for the second set; for providing an eighth signalthat represents the .[.value.]. .Iadd.sum .Iaddend.of the sixth signal.Iadd.and the seventh signal .Iaddend.divided by .Iadd.the sum of.Iaddend.the .[.seventh.]. .Iadd.fourth .Iaddend.signal .Iadd.and thefifth signal .Iaddend.to indicate a change in the electric current; forstoring said logic sets for different wire feed rates for differentchanges in current level, and for controlling the electric current inresponse to said eighth signal and the wire feed according to said logicsets.
 7. The welder described in claim 6, further characterized in thatthe wire feed is rotatable about the axis of the weld torch and includesa servo drive responsive to signals from a signal control to index thewire feed to locations on opposed sides of the puddle.
 8. The welderdescribed in claim 6, further characterized in that the imaging meansproviding successive video frames of the puddle and the signalprocessing means comprises means for determining the centerline of thepuddle from said images to provide a first centering signal .[.to.]. forcentering the weld torch over the puddle.
 9. A welder comprising a torchcontains a camera that provides sequential snapshots of a weld paddleand a controller for increasing and decreasing weld current as afunction of puddle dimensions, characterized in that the controllercomprises:means, responsive to .[.an.]. a puddle dimension signal fromthe camera indicating a puddle dimension, for summing two values fordesired current change from two adjacent fuzzy logic sets defined byrespective puddle dimensions and current change levels, and for changingthe weld current as a function of said sum, said two fuzzy logic setsbeing selected from a plurality of fuzzy logic sets for possible puddledimensions ranging from a minimum to a maximum and said two values beingdetermined as .Iadd.a .Iaddend.proportional function of the degree ofmembership in each of said two adjacent fuzzy logic sets for the puddledimension signal.
 10. A welder as described in claim 9, furthercharacterized by a wire feeder mounted on the torch and rotatablymoveable about an axis of the torch normal to the puddle.
 11. The welderdescribed in claim 10, further characterized by a motor, a shaft rotatedby the motor and a transmission coupling the shaft to the feeder, themotor being operable to rotate the shaft to move the feeder.
 12. Thewelder described in claim 9, further characterized in that thecontroller comprises means for generating a signal indicating a puddlecenterline from a plurality of successive puddle dimensions produced inresponse to successive outputs from the camera and for providing acontrol signal to reposition the torch over said centerline.
 13. Aninert electric gas welder comprising an electric current torchcontaining means for providing an image of a weld puddle, characterizedby:signal processing means operating in successive computing cycles fordetermining from the image a dimension of the weld puddle, fordetermining from stored functions the degree of membership of saiddimension in a plurality of fuzzy logic functions indicating discretechanges in weld current, said degree of membership being an alpha value,for storing a moment and area for each fuzzy logic function, forproviding for each alpha value greater than a set minimum a current.[.temp.]. moment value that is the product of the alpha for thefunction and the moment for the membership function, for providing acurrent .[.temp moment.]. .Iadd.area .Iaddend.value that is the productof the alpha for the membership function and the area for the membershipfunction, for providing, in a discrete signal processing cycle, a firstvalue that is the sum of each of said current .[.temp.]. moments and asecond value that is the sum of each of said .Iadd.current.Iaddend.areas, for providing, during a computing cycle, a third signalthat is the value of the first value divided by the second value, andfor providing a signal to the electric current torch to modify thecurrent through the electric current torch as a function of themagnitude of said third signal.
 14. The welder described in claim 13,further characterized in that there are five of said fuzzy logicfunctions for titanium wire welding said discrete changes comprising abig increase in current, a big decrease in current, an increase incurrent, a decrease in current and no change in current.
 15. The welderdescribed in claim 13, further characterized in that there aretwenty-five of said fuzzy logic functions for stainless steel wirewelding, said discrete changes comprising .Iadd.a big increase incurrent, .Iaddend.a big decrease in current, an increase in current, adecrease in current and no change in current.
 16. A welder comprisingimaging means for producing image signals indicating the length andwidth of a weld puddle beneath the torch, characterized by:signalprocessing means for providing length and width values from the imagesignals, for storing moment and area values for different discreteranges of puddle length and puddle width that identify fuzzy membershipfunctions associated with weld current levels, for selecting themembership functions associated with said length and width values, forproviding a membership signal indicating the degree of membership of thelength and width values in each of said selected associated membershipfunctions, for selecting among a pair of said length and width valuesthe one with the lowest degree of membership, for providing a momentvalue that is the product of said lowest degree of membership and one ofthe stored moment values; for providing in area signal that is theproduct of said lowest degree of membership and one of the stored areavalues, and .Iadd.for .Iaddend.providing a current signal thatrepresents the sum of all moment signals divided by the sum of all areasignals, said current signal controlling weld current.
 17. A weldingmethod characterized by:illuminating a weld puddle with a strobe lightduring welding; providing signals indicating a weld puddle dimensionbased on individual video frames of the weld puddle produced from thestrobe light on a video camera in a weld torch above the puddle; storingN membership functions, each identifying a discrete change in weldcurrent for a range of said dimensions and storing a moment value and anarea value for each membership function; providing an alpha signal foreach membership function in which said puddle dimension falls, the alphasignal indicating the degree of membership of said dimension in themembership function, based on a stored value for the function and thedimension; providing for each membership function for which an alphavalue is produced, a pair of signals indicating the product of saidalpha value and a moment and area stored for said membership function;changing weld current as a function of the sum of all said pair ofsignals for which alpha signals are produced.
 18. The method describedin claim 17, further characterized in that:a pair of alpha signals areproduced for puddle length and width respectively and the alpha signalwith the lowest degree of membership is selected to produce saidproduct. .Iadd.
 19. A welder comprising a torch, an imaging means and acontroller for controlling the weld current to the torch, characterizedin that the controller comprises signal processing means for:receivingsignals from the imaging means for determining one or more dimensions ofa weld puddle produced by the welder; determining degrees of membershipof said one or more dimensions in a plurality of adjacent fuzzy logicsets covering possible puddle dimensions ranging from a minimum to amaximum; determining from said fuzzy logic sets for which said degreesof membership are non-zero, a plurality of possible current changeamounts using a plurality of fuzzy rules; and determining a currentchange signal from the possible current change amounts by summingcurrent values of said rules, the current values being determined as aproportional function of said determined degrees of membership..Iaddend..Iadd.20. The welder of claim 19, wherein a width dimension ofthe weld puddle is determined. .Iaddend..Iadd.21. The welder of claim20, including a wire feeder which feeds titanium wire, and wherein thereare five fuzzy logic rules corresponding with five puddle width fuzzysets and providing five possible current change amounts of a big currentincrease, a current increase, no current change, a current decrease anda big current decrease. .Iaddend..Iadd.22. The welder of claim 19,wherein both a width dimension and a length dimension of said weldpuddle are determined, and wherein degrees of membership are determinedfor said width dimension in a plurality of width fuzzy logic sets, andwherein degrees of membership are determined for said length dimensionin a plurality of length fuzzy-logic sets. .Iaddend..Iadd.23. The welderof claim 22, including a wire feeder which feeds stainless steel wire,and wherein there are twenty five fuzzy logic rules corresponding withfive puddle length fuzzy sets and five puddle width fuzzy sets andproviding five possible current change amounts of a big currentincrease, a current increase, no current change, a current decrease anda big current decrease. .Iaddend..Iadd.24. The welder of claim 19,wherein said current values of said rules include current moment valuesand current area values, said current moment values and said currentarea values being determined from a multiplication of at least one ofsaid degrees of membership of said one or more puddle dimensions and amoment value or area value, respectively, associated with said possiblecurrent change amounts, and wherein said current moment values aresummed together, said current area values are summed together, and saidsummed current moment values are divided by said summed current areavalues to provide said current change signal. .Iaddend..Iadd.25. Thewelder of claim 24, wherein the current moment value and said currentarea value of a rule are determined by taking the minimum of the degreeof membership of said width dimension in the width fuzzy set associatedwith the rule and the degree of membership of said length dimension inthe length fuzzy set associated with the rule, and by multiplying thisminimum by the moment value and current area value, respectively,associated with the current change amount of the rule..Iaddend..Iadd.26. The welder of claim 19, including a wire feedermounted on the torch, the feeder being rotatably moveable about the axisof the torch normal to the weld puddle. .Iaddend..Iadd.27. The welder ofclaim 26, wherein the feeder is coupled to a shaft by a transmissioncoupling, and wherein the feeder is driven in rotation by a motorrotating the shaft. .Iaddend..Iadd.28. The welder of claim 26, andincluding a servo drive responsive to signals from the signal processingmeans to index the wire feed to locations on opposed sides of the weldpuddle. .Iaddend..Iadd.29. The welder of claim 19, wherein the imagingmeans provides successive video frames of the weld puddle, and thesignal processing means comprises means for determining the centerlineof the puddle from said images to provide a first centering signal forcentering the torch over the puddle. .Iaddend..Iadd.30. A welding methodcomprising the steps of:illuminating a weld puddle with a strobe lightduring welding; and providing signals indicating at least one weldpuddle dimension based on individual video frames of the weld puddleproduced from the strobe light on a video camera in a weld torch abovethe puddle; characterized by the steps of: storing N membershipfunctions, each identifying a degree of membership of said one or morepuddle dimensions in a plurality of fuzzy sets; relating said fuzzy setswith weld current change amounts using fuzzy rules, and storing a momentvalue and an area for each of these current change amounts; providing analpha signal for each rule which fires, the alpha signal of a ruleindicating the degree of membership of said one or more dimensions insaid fuzzy sets associated with that rule; providing for each rule forwhich an alpha value is produced, moment and area signals indicating theproduct of the alpha value for the rule with respectively the momentvalue and area value of the current change amount associated with thatrule; and changing the weld current as a function of the sum of saidmoment signals divided by the sum of said area signals..Iaddend..Iadd.31. The method of claim 30, wherein the puddle width andlength dimensions are determined, and wherein said alpha signal of arule is the lowest of the degrees of membership of the width and lengthpuddle dimensions in the width and length fuzzy sets associated withthat rule. .Iaddend.